The present invention relates to an ellipsoidal polarizing plate and a liquid crystal display.
A liquid crystal display of TN (twisted nematic) mode is widely used in combination with an active device such as a TFT (thin film transistor) or MIM (metal insulator metal) device.
The liquid crystal display of TN mode comprises a liquid crystal cell and a pair of polarizing elements.
The liquid crystal cell generally comprises a pair of substrates, rod-like liquid crystal molecules and an electrode layer. The rod-like liquid crystal molecules are provided between the substrates, and the electrode layer has a function of applying a voltage to the rod-like liquid crystal molecules. In the cell of TN mode, an orientation layer is provided on each substrate to align the liquid crystal molecules at the twist angle of 90xc2x0.
For improving the viewing angle of the liquid crystal display of TN mode, an optical compensatory sheet (phase retarder) is often placed between the liquid crystal cell and the polarizing element. In this case, the layered body of the polarizing element (polarizing membrane) and the optical compensatory sheet functions as an ellipsoidal polarizing plate. As the optical compensatory sheet, a stretched birefringent film has been conventionally used.
In place of the stretched birefringent film, an optical compensatory sheet comprising an optically anisotropic layer on a transparent substrate has been proposed. The optically anisotropic layer is formed by aligning liquid crystal molecules and fixing the aligned molecules. Since the liquid crystal molecules usually have large birefringence, an optical compensatory sheet obtained by using the liquid crystal molecules has a specific optical characteristic that cannot be obtained by the conventional stretched birefringent film. The optical compensatory sheet for a TN mode comprising discotic liquid crystal molecules is disclosed in Japanese Patent Provisional Publication No. 6(1994)-214116, U.S. Pat. Nos. 5,583,679, 5,646,703 and German Patent Publication No. 3,911,620A1, and the one comprising rod-like liquid crystal molecules is disclosed in Japanese Patent Provisional Publication No. 7(1995)-35924.
An object of the present invention is to provide an ellipsoidal polarizing plate suitable for a liquid crystal display of TN mode.
The present invention provides an ellipsoidal polarizing plate comprising a first optically anisotropic layer, a second optically anisotropic layer, a polarizing membrane and a transparent protective film, wherein the first optically anisotropic layer has an angle of 5xc2x0 to 85xc2x0 between the direction giving the maximum refractive index and the layer plane, and wherein the second optically anisotropic layer is optically positive and uniaxial, and the second optically anisotropic layer has an angle of 0xc2x0 to 5xc2x0 between the direction giving the maximum refractive index and the layer plane.
The invention also provides a liquid crystal display comprising a liquid crystal cell of TN mode and two polarizing elements arranged on both sides of the liquid crystal cell, wherein at least one of the polarizing elements is an ellipsoidal polarizing plate comprising a first optically anisotropic layer, a second optically anisotropic layer, a polarizing membrane and a transparent protective film, wherein the first optically anisotropic layer has an angle 5xc2x0 to 85xc2x0 between the direction giving the maximum refractive index and the layer plane, and wherein the second optically anisotropic layer is optically positive and uniaxial, and the second optically anisotropic layer has an angle of 0xc2x0 to 5xc2x0 between the direction giving the maximum refractive index and the layer plane.
In the present specification, the term xe2x80x9cessentially perpendicularxe2x80x9d means that the noticed angle is within the range of 90xc2x0xc2x120xc2x0. The angle is preferably within the range of 90xc2x0xc2x116xc2x0, more preferably within the range of 90xc2x0xc2x112xc2x0, further preferably within the range of 90xc2x0xc2x18xc2x0, and most preferably within the range of 90xc2x0xc2x14xc2x0.
The term xe2x80x9cessentially parallelxe2x80x9d means that the noticed angle is within the range of 0xc2x0xc2x120xc2x0. The angle is preferably within the range of 0xc2x0xc2x116xc2x0, more preferably within the range of 0xc2x0xc2x112xc2x0, further preferably within the range of 0xc2x0xc2x18xc2x0, and most preferably within the range of 0xc2x0xc2x14xc2x0.